The present invention relates to polycrystalline masses of thermally-stable self-bonded diamond and CBN compacts and more particularly to the bonding ofo these thermally-stable compacts to carbide supports.
It is well known to use diamond, cubic boron nitride (CBN) or other abrasive particles embedded in the grinding, abrading, or cutting sectionn of various tools. Also well known in this art are compacts of polycrystalline abrasive particles typified by polycrystalline diamond and polycrystalline CBN compacts. Such compacts are represented by U.S. Pat. Nos. 3,745,623 and 3,609,818 with respect to polycrystalline diamond compacts; and U.S. Pat. Nos. 3,767,371 and 3,743,489 with respect to polycrystalline CBN compacts. While such polycrystalline compacts represent a significant contribution to this art in many fields of use, thermal degradation at elevated temperature, e.g. above about 700.degree. C., did limit their usefulness, especially in metal matrix bond applications. The thermal stabilitty of such polycrystalline compacts was improved with the advent of porous (or thermally stable) self-bonded diamond and CBN compacts containing less than about three percent non-diamond phase, hereinafter often termed "porous compacts". Compacts of this type are the subject of U.S. Pat. Nos. 4,224,380 and 4,228,248.
Other thermally stable comptacts, though not "porous", include the compacts described in European Patent Publication No. 116,403, which compacts are described as comprising a mass of diamond particles present in an amount of 80 to 90% by volume of the body and a second phase present in an amount of 10 to 20% by volume of the body wherein, the mass of diamond particles containing substantial diamond-to-diamond bonding to form a coherent skeletal mass and a second phase containing nickel and silicon, the nickel being in the form of nickel and/oro nickel silicide and silicon being in the form of silicon, silicon carbide, and/or nickel silicide. British patent application No. 8508295 descibes a compact comprising a mass ofo diamond particles present in an amount of 80 to 90% by volume in the compact andn a second phase present in an amount of 10 to 20% by volume of the insert, the mass of diamond particles containing substantial diamond-to-diamond bonding to form a coherent skeletal mass and a second phase consisting essentially of silicon, the silicon being in the form of silicon and/or silicon carbide. These products are described as being thermally stable as are the porous compacts described above. Additionally, cubic boron nitride compacts which are essentially 100% dense, i.e. substantially devoid in sintering aid or catalyst content, are described in U.S. Pat. Nos. 4,188,194 and 4,289,503. These CBN compacts are thermally stable due to the absence of catalyst content.
While conventional and thermally-stable compacts already are mated to a carbide support, the carbide support can be brazed to a carbide substrate in accordance with U.S. Pat. Nos. 4,225,322 and 4,319,707. Disclosed in these Knemeyer patents are a process and apparatus which permits the use of high temperature braze alloys for attaching a composite polycrystallinen compact t a carbide substrate. Such high temperature braze alloys, in turn, provide significantly greater bond strengths. The Knemeyer process and apparatus area based on the utilization of a heat sink in contact with the polycrystalline diamond or CBN layer of the supported compact being brazed to the carbide substrate. The heat sink insures that the temperture of the diamond/CBN compact will not exceed a temperature whereat thermal degradation of the compact can occur. This means that the two carbide pieces being brazed can be heated to a temperature sufficient for the braze alloy to reach its liquidus for forming a good braze joint. Upon cooling, the two carbide pieces contract abou the same so that little residual stress is placed on the braze joint since the two carbide pieces being joined have about the same coefficient of thermal expansion. Application of the heat sink apparatus in the brazing of conventional polycrystalline diamond/CBN compacts to carbide supports has been avoided since the residual metal sintering aid therein expresses a greater coefficient of thermal expansion than does the diamond/CBN, thus making the heating of the polycrystalline compacts to elevated temperature risky since, upon cooling, cracking of the compacts often is evident.